A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head (hereinafter “head”) which is positioned over a specific location of a disk by an actuator.
A head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a head and the surface of a magnetic-recording disk must be tightly controlled. An actuator relies on suspension's force on the head to provide the proper distance between the head and the surface of the magnetic-recording disk while the magnetic-recording disk rotates. A head therefore is said to “fly” over the surface of the magnetic-recording disk.
It is important to maintain the optimal distance between the head and the disk while performing read/write operations. If the head flies too low, then the head could wear, pick up lubricant or other debris, or make physical contact with the disk. Inadvertent contact between the head and the disk during a read/write operation can result in read/write errors or damage to either the head or the disk. Too high a fly height may also result in read/write errors and may frustrate efforts to achieve a consistent fly height. Any electrical potential difference between the head and the disk may also affect the optimal fly height; therefore, it is advantageous to determine this inherent electrical potential as part of an approach for maintaining a particular fly height.